Filter Basics (47)

There are only three major components in a Web project:

Filter filter

Listener.

Servlet

In the Web, a filter is a class javax.servlet.Filter.

A filter is a response (response) that is used by an overly-worried user (request) at execution time, or by worrying about the return from the requested resource.

Implement a most basic filter

1: The filter only filters the URL (path).

2: Filter developers to achieve.

3: Filter because it is the core group of the Web, the filter's implementation must also be configured in the XML.

4: Three life cycle method: Init,destory,dofilter (Perform a worry task). Each request of the user executes the Dofilter method, and

Init,destory will only be executed once.

Init method Execution Time: The object of the filter is initialized directly at the start of the project, so the Init method is executed at Tomcat startup.

First step: Write a class to implement the filter interface

Package Cn.hongxin.filter;import Java.io.ioexception;import javax.servlet.filter;import Javax.servlet.filterchain;import Javax.servlet.filterconfig;import Javax.servlet.servletexception;import Javax.servlet.servletrequest;import Javax.servlet.ServletResponse; Public classOnefilter implements Filter {//This method only executes once when Tomcat is started     Public voidInit (Filterconfig filterconfig) throws Servletexception {System.err.println ("the filter is initialized:"+ This); }    //This method performs a worry task     Public voidDoFilter (servletrequest request, servletresponse response, Filterchain chain) throws IOException, Servlet Exception {System.err.println ("1: Performing the Over-filtration:"+ This); //executes the next filter and executes the target servlet if there is no next filterChain.dofilter (request, response);//2:System.err.println ("3: Target component, execution completed ...");}  Public voiddestroy () {System.err.println ("filter dead."+ This); }}

Step Two: Configure this filter in Web. xml

<filter>      <filter-name>one</filter-name>      <filter-class> cn.itcast.filter.onefilter</filter-class>  </filter>  <!--configure which URL to filter on -  <filter-mapping>      <filter-name>one</filter-name>      <url-pattern>/ One </url-pattern>  </filter-mapping>

Step Three: Test execution

Settings for Url-pattern in Ilter filter-mapping

Settings for Url-pattern:

/* = Request this servlet for all URLs | are being considered by this filter.

/= can only be given to Servlets. -All other URLs that are not processed by the servlet are handled by the servlet specified by this URL. The default servlet.

*.jspx = all ends with jspx request to this servlet or be intercepted by a filter. such as Http://local:8080/proj/abc.jspx

/jsps/* = All paths beginning with/jsps/are requested to this servlet or intercepted by a filter.

/jsps/*.jspx wrong: Sun rules * Both sides can not appear at the same time characters.

<filter-mapping>      <filter-name>one</filter-name>      <!--blocking over all URLs---      < url-pattern>/index.jsp</url-pattern>      <url-pattern>/jsps/*</url-pattern>      <!--intercept all URL settings on this servlet-     <servlet-name>OneSerlvet</servlet-name>  </ Filter-mapping>

Other configurations in the filter

If you have jsps/abc.jsp this page, there are two ways to display this page:

1: In the Address bar request: http://local:8080/project/jsps/abc.jsp-can be intercepted because: path conforms to/jsp/abc.jsp

2:req.getrequestdispathcer ("/jsps/abc.jsp"). Forward (REQ,RESP); -

Dipatcher Properties:

request– the default value to intercept only the user's new request.

forward– to intercept the forwarding.

include– to include interception.

Error-intercepts the errors.

<!--set to forward intercept--

<DISPATCHER>REQUEST[W1] </dispatcher>

<dispatcher>FORWARD</dispatcher>

7. Configure the initialization parameters of the filter

There is one method in the filter class: init (filterconfig config); The filtetrconfig contains the read initialization parameter value from Web. Xml.

<filter>

<filter-name>one</filter-name>

<filter-class>cn.itcast.filter.OneFilter</filter-class>

<init-param>

<param-name>name</param-name>

<param-value> Zhang San jack</param-value>

</init-param>

<init-param>

<param-name>age</param-name>

<param-value>88</param-value>

</init-param>

</filter>

Get the value in the filter class:

Private Filterconfig conf;

This method only executes once when Tomcat is started

Public void init (filterconfig conf) throws servletexception {

this. conf=conf;

System. err. println ("filter Initialized:" + this);

Get the value of name:

String name = Conf.getinitparameter ("name");

System. err. println ("name is:" +name);

System. err. println ("----------------------------");

Enumeration<string> en= conf.getinitparameternames ();

while (En.hasmoreelements ()) {

String paramname = En.nextelement ();

String val = conf.getinitparameter (paramname);

System. err. println (paramname+ "=" +val);

}

}

Filter Basics (47)